1. Field of the Invention
The invention relates to a liquid crystal display device, particularly to a liquid crystal display device having a display pixel region and a dummy pixel region adjacent thereto.
2. Description of the Related Art
A display device formed with a display pixel region formed with a plurality of pixels as liquid crystal display pixels and a dummy pixel region including dummy pixels that do not contribute to a display on a glass substrate has been conventionally known. A description will be given referring to such a display device as a “liquid crystal display device” hereafter.
A general description of the conventional liquid crystal display device will be given referring to FIG. 3. FIG. 3 is a plan view of this liquid crystal display device, showing a display pixel region 10A and its vicinity that will be described below. Data lines 2 supplying a display signal D and scanning lines 3 supplying a pixel selection signal G are formed in a grid form on a first substrate 1P that is one of two glass substrates forming the liquid crystal display device as shown in FIG. 3. A plurality of pixels 10 is respectively formed in regions surrounded by the data lines 2 and the scanning lines 3 as liquid crystal display pixels. A pixel selection thin film transistor (hereafter, abbreviated to “TFT”) 11 connected to the data line 2 and the scanning line 3 and a pixel electrode 12 connected to the pixel selection TFT 11 are formed in each of the pixels 10. The pixel 10 includes a pair of alignment films, a second substrate, a common electrode, a second alignment film, a liquid crystal layer, a retardation plate, a polarizing plate, and so on although not shown, forming the liquid crystal display pixel. A description will be given referring to a region formed with these pixels 10 as a display pixel region 10A hereafter.
Furthermore, a dummy pixel region 20A including a plurality of dummy pixels 20 is formed in a region adjacent to the display pixel region 10A on the first substrate 1P in this liquid crystal display device. The dummy pixel 20 has the structure of the pixel 10 described above and is shielded from light by a black matrix (not shown). That is, the dummy pixels 20 do not contribute to an actual display.
The formation of this dummy pixels 20 adjacent to the display pixel region 10A prevents nonuniform formation of layers forming the pixels 10 in an end portion of the display pixel region 10A and thus achieves uniform pixel formation at the end portion that are comparable with other pixels 10. That is, a difference in film thickness between the pixels 10 in the end portion and the pixels 10 on the inner side from the end portion is reduced. The dummy pixel 20 has the same electric structure as that of the pixel 10. Therefore, the electric characteristics of the pixels 10 in the end portion do not differ from those of the pixels 10 on the inner side from the end portion.
Driving TFTs sending a driving signal to the pixel selection TFTs in response to a predetermined synchronizing signal are formed adjacent to the dummy pixels 20 in a region outside the dummy pixel region 20A. The driving TFTs herein are, for example, sampling TFTs 60 supplying a display signal D that is one of the driving signals to the data lines 2. The plurality of sampling TFTs 60 is included in a horizontal driving circuit 101 serving as a driving circuit. A vertical driving circuit 102 including driving TFTs supplying a pixel selection signal G is connected to the scanning lines 3, although not shown.
Next, an operation of the liquid crystal display device will be described. First the pixel selection TFT 11 turns on in response to a pixel selection signal G supplied to the scanning line 3 through the driving TFT of the vertical driving circuit 102. Then, a display signal D supplied to the data line 2 through the driving TFT of the horizontal driving circuit 101, i.e., the sampling TFT 60, is supplied to the pixel electrode 12 through the pixel selection TFT 11. At this time, a light transmission amount of a liquid crystal layer (not shown) of the pixel 10 changes in response to the display signal D, and display light is outputted from the pixel 10 corresponding to the light transmission amount. While the dummy pixel 20 outputs display light similarly to the pixel 10, the display light is not visually recognized by a viewer since it is shielded from light by the black matrix.
The relevant technology is disclosed in the Japanese Patent Application Publication No. 2003-241683.
In the described liquid crystal display device, however, the driving TFTs, i.e., the sampling TFTs 60, need be formed in a frame of the first substrate 1P (i.e., on an end portion of the first substrate 1P where the pixels 10 or the dummy pixels 20 are not formed). Therefore, the frame of the liquid crystal display device requires the space to accommodate those device elements.